Herding Water

Herding Water

The future of water in Texas depends in great part on a byzantine process that is equal parts sophisticated computer modeling and seat-of-the-pants guesswork. In 2005, finally recognizing that water doesn’t respect geopolitical boundaries, the Legislature required local groundwater districts to get together and decide how much water should be left in their shared aquifer in 50 years. They’re supposed to figure out their “desired future conditions” by September 2010. Many of the planning groups are behind schedule.

The slow pace is not surprising: This is scientifically complicated and politically tricky work. Getting it wrong invites disaster. The desired future conditions, to be rolled into the state’s 2012 water plan, will tell groundwater districts how much water they’ll be able to allocate for the next half-century. That has serious consequences for the state’s aquifers, springs, streams, and rivers.

“It’s so much about how people envision the future,” says Al Broun, the Hays Trinity district’s volunteer geologist. “Do they want streams that still have water in them and springs like Jacob’s Well that flow?”

The Hays Trinity is one of the few districts in the state considering spring flow, says Laura Marbury of the Environmental Defense Fund. The others are basing their plans on future demand. “That’s not the way to do it,” Marbury says. “My whole take is that this process is the opportunity to do it right. They have a chance now to not overdevelop Hill Country groundwater.”

“Desired conditions” for the Trinity Aquifer are still being studied, using a computer-aided groundwater model that looks at the consequences of increased pumping. According to the latest model, If pumping went up just 25 percent, the Middle Trinity aquifer would drop an average of 17 feet across the region by 2060, and as much as 60 feet in parts of Kerr County. Springs would be sapped of 44 percent of their current discharge. Rivers could lose between 11 and 44 percent of the water that currently comes from the aquifer.

The models being studied assume that rainfall will remain constant over the next five decades, though many climate experts expect the American Southwest to enter a state of permanent drought sometime this century. Another limitation of the computer models: They work only on regional averages, so they can’t tell you what might happen to a particular well or spring like Jacob’s Well.

Given this uncertainty, conservationists like Marbury urge water planners to “be as conservative as possible because you just don’t know what the future will hold.”